Bimetallic element



May 29, 1928. 1,671,491-

H. SCOTT BIMETALLIC ELEMENT Filed Dec. 27, 1926 I Expansion.

WITNESSES: INVENTOR 514 v HowaraScoff.

Patented May 29, 1928.

I UNITED STATES PATENT OFFICE.

HOWARD SCOTT, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION" OF PENNSYLVANIA.

IBIMETALLIC ELEMENT.

Application filed December 27, 1926. Serial No. 157,822.

My invention relates to thermostatic devices and particularly to bimetallic elements therefor.

An object of my invention is to provide a bimetallic element for a thermostatic device, that shall deflect uniformly over a wide range of temperatures.

Another object of my invention is to provide a bimetallic element for a thermostatic in device in which the cooperating elements thereof have substantially equal temperature 'coefficients of expansion at relatively low temperatures but have widel different temperature coefficients of expansion at relatively high temperatures.

Another object of my invention is to provide a bimetallic element that shall have reversible deflection characteristics.

A further object of my invention is to provide a bimetallic element that shall have uniform deflection over a range of 200 C. and

A still further object of my invention is to provide a bimetallic element that shall have elastic deflection up to- 500 C.

In practicing my invention I provide a bimetallic element for thermostatic devices which comprises two cooperating alloys suitably joined together. One of the alloys contains iron and manganese, the manganese content not exceeding 30 of the alloy aggregate. T he other alloy may be one having low expansion characteristics similar to that of a nickel-iron alloy.

It is well known that pure iron, upon being heated, passes through a transformation point at approximately 900 C. and, upon still further heating, passes through a second transformation point at substantially 1400 C. 'The'stru-cture of the iron below 900 C. is commonly-known as Alpha'crystalline structure. Between 900 C. and 1400 Chthe crystalline structure of pure iron is -*-l -nown- 'as- Austen'ite 'or Gamma iron and 45, changes to thatknown as Delta lIOH.

'above' 1400' C. the crystalline structure ;,Upon being heated,"pure iron expands uniformly 'up to' 900 0'. and: hasa temperature coefficient" of- 'expansion of approximately- 12 X1 1-0'"c1n; per; degree" Qandbetween 900 Grind 1400 or between its first and second transformation points, it expands uniformly but at a rnu ch higher rate, the coefli oie'nt of expansion belng approximately 20 10 cm. per degree C. Above 1400 C. pure iron expands at a lower rate than iron having an austenitic structure.

I have found that ,analloy containing relatively pure iron and a substantial quantity of manganese possesses substantially the same expansion characteristics upon heating as iron having an austenitic crystalline structure range; that is, it follows the same expansion curve on heating as on cooling.

Between C. and about 125 (1', I have found that the manganese iron alloy has a temperature coeflicient of expansion that does not differ appreciably from that of a nickel-iron alloy, but above 125 .C. the manganese-iron alloy has a much higher temperature coeflicient of expansion. The manganese-iron'alloy, when joined with an alloy having a relatively low coeflicient of expansion to form a bimetallic element, is very useful in thermostatic devices as will hereinafter be set forth.

In the single sheet of drawings, the temperature expansion curves of two alloys and of a bimetallic element comprising these alloys are illustrated. In the drawings, the vertical scale repre sents expansion in thous'andths per unit length and the horizontal scale represents temperature in degrees C. The temperature expansion curve illustrated by numeral 11 represents the expansion characteristic of an alloy containing manganese, iron and" a minor percentage of carbop. The curve designated by numeral 12 represents the thermal expansion. characteristics of a nickel-iron alloy that forms a bimetallic element with the alloy represented by the curve 11. The curve 13, illustrated by a broken line, represents the'diffcrence in expansion between the alloyszof curves 11 and 12, to which'the deflection'of a'bimet'all'ic element composed of these'alloys' is ,directly proportional under appropriate "conditions.

Thealloy represented by curve jllflias a very high temperature coeflicient of expansion between 100 C. and"500 GA Between representedby the curve'lfl'i It is to be noted that, between 150 C. and +100 0.,

the difference in the ordinates of the curves 1'1 and 12 is substantially zero as indicated- 11 and 12 is very marked and is of a uniform character. The bimetallic element represented by the curve 13 retains an elastic expansion at a temperature of about 500 C.

The thermal characteristic of the alloy represented by thecurve 11 may be varied by changing the manganese content between the limits of substantially 15% and and by moderate additions of other alloying elements. The alloy represented by the curve 12 may be a nickel-iron alloy having any desired temperature coefiicient of expansion that is suitable for use with the manganese-iron alloy.

I have found that a bimetallic element comprising a 515%- nickel-iron alloy and a ferrous alloy containing substantially 23% manganese and .1% carbon is very sensitive to changes in temperature between the temperatures of substantially 150 C. to 400 C.

Between 150 C. and 150 C., this bimetallic element has, for practical purposes, zero expansion. Therefore, it is not subjected to high mechanical stresses in this temperature range.

It is to be understood that the nickel content of the alloy represented by curve 12 may be varied in accordance with the amount of manganese or other additional alloying elements in the allo represented by curve 11 in order that a bimetallic element may be obtained for. thermostatic devices that is operable over a relatively wide range of temperatures in which it is to be responsive, and that is substantially non-responsive to temperatures which are not included within the desired operating range.

While I have designated the curve 12 as being representative of the temperature expanslon characteristic of a ferrous alloy containing nickel, I do not wish to be limited to use of this alloy as other alloys hav- 'ing a low temperature coefiicient of expan- 'sion may be employed. However, the nickel content of the alloy mentioned above may in some inst. ces be materially lessthan of the alloy aggregate.

Various modifications may be made in the device embodying my invention without departing from the spirit and scope thereof. I

desire, therefore, that only such limitations quantity of nickel.

3. A thermostatic element comprising metals having different coeflicients of expansion, one of said elements being a ferrous alloy containing substantial amounts of nickel and the other of said elements being aferrous alloy containing a substantial quantity of manganese.

and the other of said elements being an ailoy containing a substantial 4. A thermostatic element comprising metals having different coefiicients of expansion, one of said elements being a ferrous alloy containing substantial amounts of nickel and the other of said elements being an alloy containing carbon, and maganese,

said manganese content being'predominant.

5. A thermostatic element comprising two metallic elements having diiferent coefiicients of expansion, oneof said elements being a ferrous alloy containing not less than 15% of manganese, and the other of said elements being a nickel-iron alloy.

6. A thermostatic element comprising two metallic elements having different co'efiicients of expansion, one of said elements containing not more than 30% manganese, and the other of said elements being a ferrous alloy containing a substantial quantity of nickel. i

7. A thermostatic element comprising two metallic elements having different coefiicients of expansion, one of said elements containing from 15% to 30% of manganese, and the other of said elements being an alloy containing a substantial quantity of nickel. i

e 8. A thermostatic element comprising two metallic elements having difierent coeflicients of expansion, one of said elements being an alloy containing manganese and carbon, the manganese content being not less than 15%, and the other of said elements being an alloy containing a substantial quantity ofnickel.

9. A thermostatic element comprising two metals having different tem erature coefficients of expansion, one of Sflld, metals being a ferrous alloy containing substantially 45% nickel, and the other metal being an alloy containin substantiall 23% of manganese, 0.1% 0 carbon, an iron.

Intestimony whereof,tI have hereunto subscribed my name this 21st day of December, 1926. I

HOWARD score 

